One of the rarest of Earth's astronomical events is a ghostly glow called the zodiacal light that the ancient Greeks believed was caused by distant volcanic eruptions. Visible in the Northern Hemisphere for the next two weeks, the phenomenon — caused by sunlight scattering off countless grains of microscopic interplanetary dust spread out to beyond the orbit of Mars — will be visible above the western horizon as a faint cone of light that extends halfway up the sky for about an hour after sunset.

The vast majority of the interplanetary dust is concentrated within the plane of the inner solar system near the sun, making the dust grains combined with light appear along the ecliptic, the path in the sky each planet follows.